Make column for same line original scope positions relative

Part of aligning with tc39/ecma426#188.

Author: szuend

src/decode/decode.ts

@@ -47,6 +47,7 @@ export function decode(
 
 const DEFAULT_SCOPE_STATE = {
   line: 0,
+  column: 0,
   name: 0,
   kind: 0,
   variable: 0,
@@ -214,9 +215,14 @@ class Decoder {
 
   #handleOriginalScopeStartItem(item: OriginalScopeStartItem) {
     this.#scopeState.line += item.line;
+    if (item.line === 0) {
+      this.#scopeState.column += item.column;
+    } else {
+      this.#scopeState.column = item.column;
+    }
     const scope: OriginalScope = {
-      start: { line: this.#scopeState.line, column: item.column },
-      end: { line: this.#scopeState.line, column: item.column },
+      start: { line: this.#scopeState.line, column: this.#scopeState.column },
+      end: { line: this.#scopeState.line, column: this.#scopeState.column },
       isStackFrame: false,
       variables: [],
       children: [],
@@ -256,6 +262,11 @@ class Decoder {
 
   #handleOriginalScopeEndItem(line: number, column: number) {
     this.#scopeState.line += line;
+    if (line === 0) {
+      this.#scopeState.column += column;
+    } else {
+      this.#scopeState.column = column;
+    }
 
     const scope = this.#scopeStack.pop();
     if (!scope) {
@@ -265,7 +276,10 @@ class Decoder {
       return;
     }
 
-    scope.end = { line: this.#scopeState.line, column };
+    scope.end = {
+      line: this.#scopeState.line,
+      column: this.#scopeState.column,
+    };
 
     if (this.#scopeStack.length > 0) {
       const parent = this.#scopeStack.at(-1)!;

src/encode/encoder.ts

@@ -81,6 +81,9 @@ export class Encoder {
 
     let flags = 0;
     const encodedLine = line - this.#scopeState.line;
+    const encodedColumn = encodedLine === 0
+      ? column - this.#scopeState.column
+      : column;
     this.#scopeState.line = line;
     this.#scopeState.column = column;
 
@@ -103,7 +106,7 @@ export class Encoder {
     if (scope.isStackFrame) flags |= OriginalScopeFlags.IS_STACK_FRAME;
 
     this.#encodeTag(EncodedTag.ORIGINAL_SCOPE_START).#encodeUnsigned(flags)
-      .#encodeUnsigned(encodedLine).#encodeUnsigned(column);
+      .#encodeUnsigned(encodedLine).#encodeUnsigned(encodedColumn);
     if (encodedName !== undefined) this.#encodeSigned(encodedName);
     if (encodedKind !== undefined) this.#encodeSigned(encodedKind);
     this.#finishItem();
@@ -130,12 +133,15 @@ export class Encoder {
     this.#verifyPositionWithScopeState(line, column);
 
     const encodedLine = line - this.#scopeState.line;
+    const encodedColumn = encodedLine === 0
+      ? column - this.#scopeState.column
+      : column;
 
     this.#scopeState.line = line;
     this.#scopeState.column = column;
 
     this.#encodeTag(EncodedTag.ORIGINAL_SCOPE_END).#encodeUnsigned(encodedLine)
-      .#encodeUnsigned(column).#finishItem();
+      .#encodeUnsigned(encodedColumn).#finishItem();
   }
 
   #encodeGeneratedRange(range: GeneratedRange): void {

src/roundtrip.test.ts

@@ -57,6 +57,12 @@ describe("round trip", () => {
     assertCodec(builder.build());
   });
 
+  it("handles scopes that start on the same line", () => {
+    builder.startScope(0, 5).startScope(0, 10).endScope(10, 5).endScope(10, 10);
+
+    assertCodec(builder.build());
+  });
+
   it("handles scope names", () => {
     builder.startScope(0, 0, { name: "foo" }).startScope(10, 0, { name: "bar" })
       .endScope(20, 0).endScope(30, 0);